Over time and through repeated use, bones and joints can become damaged or worn. For example, repetitive strain on bones and joints (e.g., through athletic activity), traumatic events, and certain diseases (e.g., osteoarthritis) can cause cartilage in joint areas, which normally provides a cushioning effect, to wear down. When the cartilage wears down, fluid can accumulate in the joint areas, resulting in pain, stiffness, and decreased mobility.
Arthroplasty procedures can be used to repair damaged joints. During a typical arthroplasty procedure, an arthritic or otherwise dysfunctional joint can be remodeled or realigned or an implant can be implanted into the damaged region. Arthroplasty procedures may take place in any of a number of different regions of the body, such as a knee, a hip, a shoulder, or an elbow.
One type of arthroplasty procedure is a total hip arthroplasty (“THA”) procedure, which consists of replacing both the acetabulum, also known as acetabular cup, and the femoral head with prosthetic implants. Another type of arthroplasty procedure is a hemi or half hip replacement, which consists of replacing just the femoral head with a prosthetic implant. The hip joint may have been damaged by, for example, arthritis (e.g., severe osteoarthritis or degenerative arthritis), trauma, or a rare destructive joint disease. Typically, a THA procedure is conducted to relieve pain due to osteoarthritis or to remedy severe joint damage as part of hip fracture treatment.
The hip is one of the largest joints in the human body. The hip consists of a ball and socket, wherein the socket is formed by the acetabulum, which is part of the pelvis bone. The ball, in the ball and socket system, is the femoral head, which is at the proximal end of the femur. The surfaces of the ball and socket are covered with articular cartilage, a smooth tissue that cushions the ends of the bones and enables femoral head and the acetabulum to move easily. A thin tissue called synovial membrane surrounds the hip joint. In an otherwise healthy hip joint, this membrane makes a small amount of fluid that lubricates the cartilage and eliminates almost all friction during hip movement. Bands of ligaments connect the ball to the socket and provide stability to the joint.
During a THA procedure, a damaged portion of bone in the femoral head may be removed and replaced with a femoral prosthesis or implant, and a damaged portion of the bone and cartilage in the acetabulum may be removed by reaming, scraping, cleaning or otherwise preparing of the acetabular surface to receive an implanted prosthesis, such as a prosthetic acetabular cup. After the damaged portion of the femoral head is removed, the femoral prosthesis, which includes a stem, may be cemented or simply press fitted into the patient's femur. Similarly, the acetabular cup may be screwed, pinned, cemented, or otherwise coupled to the patient's acetabulum. The acetabular cup can additionally include an osseointegrated surface to enhance the fusion of the bone to the implant. The interface between the acetabular cup and the femoral prosthesis is the ball and socket joint, or the articular interface. The specifications for the articular interface (e.g., make, model, size, material) vary depending on the patient's bony anatomy, health, activity level, and associated risks involved with the procedure.
Implants that are implanted into a damaged region may provide support and structure to the damaged region and may help to restore the damaged region, thereby enhancing its functionality. Prior to implantation of an implant in a damaged region, the damaged region is prepared to receive the implant. For example, in a hip arthroplasty procedure, one or more of the bones in the hip area, such as the femur and/or the acetabulum, may be treated (e.g., cut, drilled, reamed, and/or resurfaced) to provide one or more surfaces that can align with the implant and thereby accommodate the implant.
Accuracy in implant alignment is an important factor to the success of a THA procedure. Preparing a patient's acetabulum for implanting of a prosthetic acetabular cup can be challenging because of the unique contouring shape of the patient's acetabulum, and because the pelvic bone does not easily lend itself to resections, as in an arthroplasty procedure involving implants to the femur or tibia. These factors underscore the importance of properly preparing the acetabulum prior to a THA procedure and properly aligning the acetabular cup to the acetabulum. A one to two millimeter translational misalignment may result in imbalanced ligaments and thus may significantly affect the outcome of the procedure. For example, implant misalignment may result in intolerable post-surgery pain and also may prevent the patient from having stable leg flexion. In particular, the patient's joint may not be restored to its natural alignment with respect to the knee and ankle centers, which can result in pain and difficulty in adjustment to the new alignment.
To achieve accurate implant alignment, prior to treating (e.g., cut, drilled, reamed, and/or resurfaced) any regions of a bone, it is important to correctly determine the location at which the treatment will take place and how the treatment will be oriented. In some methods, an arthroplasty guide may be used to position and orient a resection, sawing, or implantation instrument, such as a cutting, drilling, reaming, resurfacing, or impacting instrument on the regions of the bone. The arthroplasty guide may, for example, include referencing rods and one or more apertures and/or slots that are configured to accept such an instrument. However, under some methods, it is difficult to determine the proper orientation of an arthroplasty guide and ultimately of the positioning and alignment of an acetabular cup implant. Some methods utilize arthroplasty guides to provide orientation of the treatment relative to the regions of the bone. However, such guides often rely on a human to subjectively determine or “eyeball” rotational angles and the extent of the treatment. For example, when performing an acetabular cup implantation into the hip region of a patient, many guides rely on a surgeon to determine the proper orientation of the guide as well as how much of the bone to remove when mating the implanted prosthesis to the bone. More particularly, once a surgeon has begun reaming a patient's acetabulum or impacting/implanting the acetabular cup, it can be difficult and damaging to accurately stop the reaming or impacting/implanting and start anew.
Accordingly, there is a need in the art for a customized arthroplasty acetabular cup positioning guide, and surgical systems and methods for generating and employing the acetabular cup positioning guide that increases the accuracy of arthroplasty procedures.